Sans collapsed, and he started to transform. However, Undyne burst into the clearing, and, spotting Sans writhing in the middle, she went and pinned him down. He stopped after a few seconds, and slowly slid open his eye sockets. He saw Undyne, and gave a yelp of surprise. Undyne smacked him and yelled, "SANS! What are you doing!? You knew this would happen, didn't you!"
"Y-yeah... "
"THEN WHY DID YOU RUN OFF- Oh. OH. Sans. Explain. NOW."
"I-I.." he stuttered, before a blue light filled his left eye. The air was filled with the smell of ozone. He looked panicked. He tried to get up, but Undyne kept him down. Suddenly, his spine arched in an impossible position with a loud snap. Sans said, "NOt..SafE..RuN.." before he started convulsing. Undyne backed away, a look of horror on her face. Papyrus rushed in, only to also stand and gape in mute shock. Sans screamed. He writhed, screaming as his body convulsed in a series of horrifying snaps and pops. His screams became increasingly animalistic as his body warped. After what seemed like an eternity, he stopped. He tried to pull himself up, and stood wobbling on four giant skeletal legs. Papyrus looked into the eyes of his huge, malevolent skull and said, "S-Sans..? Are you in there..?" When Sans didn't move, Papyrus put a hand up and took a tentative step forward. Sans lowered his skull to the ground, staring straight at Papyrus. He grunted, clearly trying to speak. He tried again, this time making a growling sound intermixed with the brothers' "secret language"." Papyrus, can you understand me now?"
"I can understand you, brother. But can you understand me, or do I..?"
"Nah, I can hear you fine Pap. But can you translate for me? I can't exactly tell Undyne what's going on."
"Sure, brother!"
"Wait wait wait wait. What's going on?" Undyne interjected.
"Sans wants me to translate for him, as he can't exactly tell you what going on at the moment."
"Oh, okay Papyrus. Go ahead."
"Okay Sans, what do you need me to say first?" Suddenly, Papyrus's phone started ringing. He picked up and said, "This is the Great Papyrus speaking. Who is this?"
"H-Hi. It's m-me, Alphys. I believe I may have a way to translate Sans's speaking straight into a computer? J-Just give me one second.."
"Oh, Alphys, that would be great!" he said, lowering the phone from his ear.
"What did Alphys say, bro?"
"She said that she would be here with a translator so that we could translate what you say exactly into a computer."
"I like that. Well, now we just have to wait."
"Indeed we do, brother. Indeed we do."